Untitled - The Alfred Russel Wallace Website

xxin ANIMAL MIGRATIONS 367
naturalists to certain transits or migrations of the
adult insects across the Amazon, such as have
already been noticed by Messrs. Edwards, Wallace,
and Bates, and perhaps by other travellers. The
first time I fell in with such a migration was in
November 1849, near the mouth of the Xingii,
when I was travelling up the Amazon from Para to
Santarem ; and it is thus sketched in my Journal :-
"... As we returned to the brig we saw a vast
multitude of Butterflies flying .across the Amazon,
from the northern to the southern side, in a direction
about from N.N.W. to S.S. E. They were evidently
in the last stage of : fatigue some of them attained
the shore, but a large proportion fell exhausted into
the water, and we caught several in our hands as
were all of
they passed over the canoe. They
common white and orange-yellow species, such as
are bred in cultivated and waste grounds, and having
found no matrix whereon to deposit their eggs
to the northward of the river (the leaves proper
for their purpose having probably been already
destroyed, or at least occupied, by caterpillars), were
going in quest of it elsewhere."
The very little wind there was blew from between
E. and N.E.; therefore the butterflies steered their
course at right angles to it ; and
this was the case in
subsequent flights I saw across the Amazon, although
when the wind was strong the weaker-winged insects
made considerable leeway, and would doubtless most
of them succumb before reaching land. But tin:
most notable circumstance is that the movement is
always southward, like the human waves which from
the earliest times seem to have surged one after the
other over the whole length of America, generating